1. Field of the Invention
This invention relates to composite synthetic paper excellent in printability, tear resistance, waterproofness, sewing properties (sewability), and opacifying properties. The composite synthetic paper of the present invention is useful as material for aprons, shop curtains, disposable clothing, maps, outdoor posters, signboards, hangers, flags, etc.
2. Discussion of the Background
Synthetic paper comprising a biaxially stretched thermoplastic resin film as a base layer and a uniaxially stretched thermoplastic resin film containing an inorganic fine powder as a paper-like layer is described in U.S. Pat. No. 4,318,950; JP-B-46-40794 (the term "JP-B" as used herein means an "examined published Japanese patent application"); JP-B-50-29738; JP-B-50-28114; JP-B-53-6676; JP-B-52-30390; JP-A-54-74842 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"); JP-A-56-21830; JP-A-56-118437; JP-A-56-141339; JP-A-57-149363 and JP-A-57-181829.
Coated paper with improved offset printability which is prepared by coating the above-mentioned synthetic paper with a surface modifier is also available. The surface modifier (primer) includes an aqueous solution of polyethyleneimine, a cationic or amphoteric acrylic polymer containing a tertiary or quaternary nitrogen atom, poly(ethylene-urea), an epichlorohydrin adduct of polyamide, etc., as disclosed in U.S. Pat. Nos. 4,097,645; 4,420,539 and 4,906,526.
Synthetic paper having such a multi-layered structure has high mechanical strength owing to its base layer comprising a biaxially stretched film, is light on account of numerous microvoids formed around inorganic fine particles in its paper-like layer and base layer on stretching, and has excellent ink absorption and ink adhesion due to fine cracks formed on the surface of the paper-like layer upon stretching. Due to these properties, it is useful in applications demanding durability, such as posters, maps, calendars, tracing paper, surface decorative materials, catalogues, labels, and so on.
Synthetic paper with a pearl-like surface comprising an inorganic fine powder-containing thermoplastic resin biaxially stretched film as a paper-like layer is also available (cf. JP-B-49-1782; JP-B-54-31032 and U.S. Pat. No. 3,775,521).
Synthetic paper comprising (1) a support composed of (1a) a biaxially stretched thermoplastic resin film as a base layer, (1b) a uniaxially stretched thermoplastic resin film containing 8 to 65% by weight of an inorganic fine powder as a surface layer, and (1c) a backing layer; (2) a transparent thermoplastic resin film containing no inorganic fine powder provided on surface layer (1b); and (3) a primer coat having an antistatic function provided on layer (2) is disclosed in JP-A-61-3748 and U.S. Pat. No. 4,663,216.
The above-mentioned synthetic paper comprising a stretched inorganic fine powder-containing resin film has a void volume of 10 to 40% and a density of 0.60 to 1.1 g/cm.sup.3. Such synthetic paper is commercially sold from Oji Yuka Goseishi Co., Ltd. under the tradenames of "YUPO FPG", "YUPO KPG", "YUPO SCG", "YUPO FBD", "YUPO SGE", and "YUPO GFG" and from BXL Co., G.B. under a tradename of "POLYART II".
However, the thermoplastic resin stretched film in the above-mentioned synthetic paper shows highly oriented crystallinity due to stretching at a stretch ratio of 4 to 8 in the machine direction and of from 5 to 12 in the transverse direction, with the orientation being mostly in two directions. Therefore, when applied to uses involving sewing, such as curtains, diaper covers and other waterproof products, if the direction of an external stress by a needle or a thread applied to the synthetic paper is the same as the orientation direction, the synthetic paper tears easily along the orientation direction.
Further, when the synthetic paper is perfected (printed on both sides) and used outdoors, for example as hanging posters, signboards, flags or shop curtains, the print on one side shows through and overlaps the print on the other side.
In order to overcome these defects, JP-B-3-74180 proposes sewable composite synthetic paper comprising (A) a fibrous sheet obtained by press heating non-woven fabric comprising short fibers or a fiber-reinforced sheet obtained by scattering a thermoplastic resin powder and/or laminating a thermoplastic resin sheet on that non-woven fabric followed by bonding together by press heating and having adhered thereon (B) a multi-layered synthetic paper composed of a biaxially stretched thermoplastic resin film as a base layer and a uniaxially stretched thermoplastic resin film containing 8 to 50% by weight of an inorganic fine powder as a paper-like layer, with the non-woven fabric layer of (A) as a back surface layer and the paper-like layer of (B) as a surface layer. This composite synthetic paper has been put to practical use as decorative paper, book covers, bookmarks, etc.
In the above-described composite synthetic paper, the non-woven fabric and the multi-layered synthetic paper are bonded with a solvent type adhesive or a hot-melt adhesive by means of pressure rollers so that the pattern of the non-woven fabric appears on the surface of the synthetic paper as an embossed pattern (appearance of a weave pattern on the surface will hereinafter be called strike-through). Such synthetic paper with a strike-through pattern is suitable as decorative paper, bookmarks or book covers as stated above. However, when this type of synthetic paper is printed for use as hangers, posters, signboards, etc., the strike-through pattern unfortunately reduces the gloss of the print.